In a multilayer printed wiring board with embedded capacitor circuit (element), one or more insulating layers as an inner layer of the multilayer printed wiring board have been used as dielectric layers. As disclosed in Patent Document 1, circuits having a top electrode and a bottom electrode arranged to face each other on both sides of an inner-layer circuit are used as a capacitor circuit. Therefore, such capacitor circuit has been called an embedded capacitor circuit.
Capacitors are required to have the largest capacitance as possible for basic quality because they have been saved excess electric power and the like in electronic and electrical equipment. The capacitance (C) of a capacitor is calculated by the equation C=∈∈0 (A/d) (∈0 is a permittivity in a vacuum). In particular, such a demand has been required on printed wiring boards also because of the recent trends for miniaturization of electronic and electrical equipment. However, it is clear that there is a limit in improvement with surface area (A), because it is almost impossible to ensure a wide area of a capacitor electrode in a given area of a printed wiring board. Therefore, to increase the capacitance of a capacitor, in the given surface area (A) of a capacitor electrode and the specific permittivity (∈) of a dielectric layer, reducing the thickness (d) of a dielectric layer or arrangement in the layer construction of the whole capacitor circuit are required.
[Patent Document 1] U.S. Pat. No. 6,541,137
However, when a nickel-phosphorus alloy layer is provided on a surface of a bottom electrode, the problem of de-lamination between a dielectric layer and the nickel-phosphorus alloy layer caused by poor adhesion between a dielectric layer and the nickel-phosphorus alloy layer may sometimes occur. It may increase capacitance deviation from the specified capacitance and it may not meet with designated quality. Furthermore, the insufficient adhesion can be a trigger of de-lamination in a printed wiring board. Also it can be a cause of interlayer de-lamination due to thermal shocks in solder reflow and the like or de-lamination due to heat generation in operation, which are causes of shorter product life.
Therefore, a material for forming a capacitor layer having a new conductive layer for forming a bottom electrode with excellent adhesion with a dielectric layer which is capable for use as an electrode and also serves as a resistance circuit and the like was required in the market.